1. Field of the Invention
The present invention relates to an electrical double layer capacitor, and in particular, relates to a large capacity electrical double layer capacitor using polarizing electrodes.
2. Description of the Related Art
A conventional electrical double layer capacitor will be explained referring to FIG. 12. This electrical double layer capacitor is formed by one basic cell 55 or by two or more basic cells 55, where the basic cells 55 comprises separators 51, pairs of polarizing electrodes 52 and 52 that are disposed so as to contact respective separators 51 on both sides thereof, a pair of collectors 53 and 53 that are disposed so as to contact the surface of these polarizing electrodes 52 and 52 opposite to those of the respective separators 51, and gaskets 54 disposed in proximity to the polarizing electrodes 52 and 52 (FIG. 12 shows a two layer lamination).
The above separator 51 comprises a porous film that is non-electron conducting, and ion permeable.
The above polarizing electrodes 52 and 52 use a solid activated carbon having as a main component the activated carbon/polyacene material disclosed in Japanese Unexamined Patent Application, First Publication, No. Hei 4-288361.
The above collector 53 is a rubber or plastic that includes a conductive carbon, and during assembly, is crimped to the polarization electrode 52.
The above pair of polarization electrodes 52 and 52 face each other across the separator 51, and as a result, the collectors 53 and 53 are disposed respectively on both outside surfaces of the pair of polarizing electrodes 52 and 52. In addition, the gasket 54, which has a frame structure, is disposed so as to enclose the polarizing electrode 52, the separator 51, and the polarizing electrode 52 in a direction perpendicular to the direction of their arrangement, and thereby contact the collectors 53 and 53 on both sides so as to enclose an inner cell 56 that is filled by a hydrous (for example, sulfuric acid) or organic electrolyte solution 56a.
The gasket 54 and the collectors 53 used here can utilize a structure wherein the sizes of their external dimensions are the same, like the electrical double layer capacitor disclosed, for example, in Japanese Unexamined Patent Application, First Publication, No. Hei 4-237109 and Japanese Unexamined Patent Application, First Publication, No. Hei 4-280517, or a structure wherein the sizes of the external dimensions of the gasket are larger than those of the external dimensions of the collectors, like the electrical double layer capacitor disclosed in Japanese Unexamined Patent Application, First Publication, No. Hei 8-78291.
Because the withstanding voltage of the two layered electric capacitor is limited by the electrolytic voltage of the electrolytic solution 56a, depending on the required withstanding voltage, the electrical double layer capacitor can be formed by layering in plurality the basic cells 55 and connecting them serially. Furthermore, in order to reduce the resistance to adhesion, pressure is applied between the terminal electrodes disposed on both sides of the layered basic cells 55, 55, . . . , and additionally, a pressure plate is applied to both sides of a terminal electrode, and thereby the basic cells 55, 55, . . . , are retained by a constant pressure.
Recently, new uses have been being discovered and tested for the above two layered electric capacitor due to increasing capacity and decreasing equalizing serial resistance (ESR) by using polarizing electrodes 52. Examples are use in combination with a lead battery to form a starter motor drive power source for an automobile, and use in combination with a solar battery as a supplementary power source.
However, this type of electrical double layer capacitor has the problem that while pressure is applied in order to reduce the resistance to adhesion, at the same time, fractures occur in the collectors due to the force received from the polarizing electrodes and gaskets, and the inner cell is exposed to the outside via these fractures, and the electrolyte solution leaks to the outside.
In contrast, while the technological conception is different, in Japanese Unexamined Patent Application, First Publication, No. Hei 3-99422, a electrical double layer capacitor is disclosed in which a solid polarizing electrode is chamfered at the end facing the separator, and thus does not damage the separator.